This invention relates to structural support systems, and has particular application to top-supported steam generators.
Relatively large vapor generators, such as steam generating units used by utility companies, are usually hung from a frame in order to allow for thermal expansion of their components during their operation. Such frames include upstanding members disposed adjacent the front, rear and sides of the steam generator, and a laterally extending member disposed adjacent the roof of the steam generator. A plurality of tie rods are employed to hang the steam generator from its upper extremities, being connected between the roof of the vapor generator and the laterally extending frame member. A plurality of ties can also be used to connect the steam generator from its front, rear and sides to the upstanding frame members. When these ties are used the steam generator is spaced from the upstanding frame members, with the ties being disposed within the space therebetween. It is to be understood that steam generators possess certain characteristics which distinguish them from other type of large top-supported machines, and therefore lend themselves to the use of the present invention, whereas other large devices may not be suited for such use. Steam generators are generally large devices of great mass, often standing well over 150 ft. high. Yet the boundary walls of a steam generator are relatively flexible members. Because of these characteristics, top-supported steam generators have relatively low natural frequencies, tending to react to excitation frequencies of 1 cycle per second or lower.
The dynamic loading toward which the present invention is directed principally takes place during earthquakes and/or wind loading. The excitation frequencies associated with an earthquake usually are higher than the natural frequencies of the steam generator. Therefore, the steam generator tends to remain stationary, during an earthquake while its base moves.
It has been suggested to tie the steam generator rigidly to the upstanding support members in an attempt to transmit dynamic loads from the support system to the steam generator, and thereby relieve the support system of certain stresses. However, when this is done, the steam generator must be specially designed and constructed to withstand such loads which are transmitted from the support system.
As an alternative it has been suggested to employ ties which are designed to disconnect or break during the initial period of response by the steam generator to dynamic loading by the support system, thereby allowing the steam generator to be in a free-swinging mode. This approach virtually eliminates dynamic loading of the steam generator but can result in large displacement of the steam generator relative to the support system, thereby requiring that the support system be designed to accommodate relatively high stresses.
The present invention provides an apparatus and method for transmitting dynamic load from a structural support system to a top-supported steam generator, and for dissipating energy so as to lessen stresses on both the support system and the steam generator. The steam generator is dynamically isolated from the support system through the use of a plurality of dampers connected therebetween. A typical top-supported steam generator has a large mass and tends to serve as a "support" to a deflected support system which tends to "lean" against the steam generator; as a consequence, the support system experiences relatively little deflection and stress while the energy introduced to the support system during an earthquake is dissipated in the dampers.